The present invention relates to a horizontally opposed multiple cylinder engine and, more particularly, to a gas baffle provided for the horizontally-opposed multiple-cylinder engine for improving flow of gas generated in a crank chamber during an engine operation.
It is generally known to be better to utilize the horizontally-opposed multiple-cylinder engine, in which mutually opposing pistons assembled in the corresponding cylinders are symmetrically operated, to carry out so-called boxer-type operation, in consideration of engine balance during the engine operation.
In multiple cylinder engines in which boxer-type piston operation is carried out, when the mutually opposed pistons are moved from top dead centers to bottom dead centers, gas remaining in a space between opposed pistons in the crank chamber of the engine is compressed and blasted towards a low gas pressure area in the crank chamber.
This gas blasting pressure is low during low engine speed operation or steady engine speed operation. In such operation, the gas blasting pressure hardly affects an oil surface of lubrication oil stored in an oil pan. However, during high engine speed operation, the lubrication oil may be forced upwardly and rearwardly in the engine by the gas blasting pressure. This causes to rise the oil level of the lubrication oil stored in the rear portion of the oil pan and, to increase the lubrication oil temperature, the raised portion of the lubrication oil is splashed by crank weights and the temperature of the lubrication oil is raised. Moreover, the oil may be agitated so that air bubbles may be formed in the lubrication oil which is then sucked into a strainer, resulting in the lowering of the lubrication oil pressure or the degradation of the engine performance.
In order to obviate these defects or problems, the prior art provides a technique disclosed, for example, in the Japanese Utility Model Laid-open Publication No. 63-102916, in which a baffle plate is interposed between lubrication oil stored in the oil pan and the crank chamber to shut out the gas blasting pressure by the baffle plate. However, in this prior art, when the downstream side of the crank chamber is entirely shut off by the baffle plate, a gas pressure in the crank chamber increases. Particularly, during high engine speed operation, the gas pressure cannot escape and, hence, a so-called pumping loss is caused, resulting in degradation of the engine output performance.
As a countermeasure to this defect, it is considered to locate the baffle plate to shut out only a part of the gas blasted towards the lubrication oil surface. However, in this case, the gas blasting pressure is partially increased and smooth gas flow is not expected. Accordingly, in this countermeasure, such problems as described above will also not be completely solved.